The present invention relates generally to vaporizing type combustors for use in gas turbines.
Gas turbine combustors are very efficient and capable of high performance emissions and life when fueled with jet fuels, kerosene or natural gas. Performance and emissions are acceptable with fuels as heavy as No. 2 diesel fuel, for example, although life problems may be caused by carbon deposits which result from heavier and more aromatic fractions. Such life problems, however, can generally be overcome by attention to design details.
Serious problems, however, can result when attempting to use so called residual fuels. Fuels of this nature are extremely difficult to atomize to the very fine droplets required for substantially free combustion. In order to assist in atomization or vaporizing, high power external air systems, or generally high pressure systems have been used. When burning or using residual fuels in vaporizing combustors, it has been found that carbon deposits are likely to be produced which can break off as "clinkers". Similar problems are encountered with certain heavy syncrudes made, for example, from coal or shale, unless refined to a high degree by hydrogenation. This treatment increases fuel cost and requires greater capital investment. Operation on slurries of powdered low sulphur, low ash coal and oil, even though desirable, would entail similar problems, and therefore is less desirable than better grades of fuel.
Vaporizing type combustors previously used and known in the art include the use of so called fuel vaporizing tubes. The vaporizing tubes are operable to receive a fuel-air mixture and subject the same to heat for at least partial vaporization of fuel, the mixture then being exhausted into a combustor or burner of, for example, an annular vaporizing combustor of a type being developed by the assignee of the present application.
An example of this type of gas turbine combustor is disclosed in U.S. Pat. No. 4,030,288, owned by a common assignee with the present application, U.S. Pat. No. 3,913,318, U.S. Pat. No. 3,757,522 and others. Fuel vaporizing tubes shown in these prior patents have included so called "candy cane types" or "T-type", the "T-type" being a double armed candy cane configuration. Problems have sometimes existed when using such vaporizing tubes and burners, and especially it has been found that carbon may form in various parts of the vapor tube per se, and/or on other parts of the burner such as head plates, or splash plates.
Such carbon can build up and may break away and cause erosion, or flow may be impeded. Other problems or difficulties in operation and function have also occurred.
A co-pending application assigned to a common assignee herewith, namely application Ser. No. 860,644, filed Dec. 14, 1977, and entitled FUEL VAPORIZING COMBUSTOR TUBE, teaches an improved fuel vaporizing tube which provides greater life and reliability, and at least in part overcomes problems resulting from formation of carbon.